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TMDS351: Design question TMDS351 SDA/SCL

Danny Wenzel
Prodigy 20 points

Part Number: TMDS351
Other Parts Discussed in Thread: TS3DV642,

Hallo,

i'm designing a pcb with 3 HDMI inputs and and HDMI output.

At first i tried to manage everything with 2 TS3DV642 ic but ran into problems with HDMI design guidelines. It worked but caused picture problems on output display.

So i decided to use a TMDS351 instead as it is much easier to route the traces.

I also bought a SamsungTV PCB as reference to see how they used the TMDS351. At the moment i don't understand why they use an ic at each SCL/SDA pair.

Why can't i route the traces like on the TS3DV642 directly?

The 3 inputs will always be there. They can't be plugged out.

The pcb will replace a module in a bmw. The inputs are 1. RGsB to HDMI converter for oem system picture, 2. HDMI from Raspberry Pi, 3. AV to HDMI converter for picture from rearcam.

I want to keep the design as easy as possible.

Regards

  • 0
    TI__Guru**** 183551 points

    It would depend on your system design requirement.

    One example I could give is the HDMI DDC capacitance requirement. Typically the HDMI cable capacitance would exceed the HDMI DDC capacitance requirement, and then you would need to use an I2C level shifter to isolate the cable capacitance in order to meet the capacitance requirement.

    Second example is some sources may have DDC in a voltage domain that is different from the sink DDC voltage domain. In this case, you would also need to have a level shifter to shift between the two voltage domains.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 20 points

    Thx for the explanation.

    But why does the TS3DV642 not need the level shifters?

    As it worked without level shifters on TS3DV642 i guess it will also work without on TMDS351.

  • 0 in reply to Danny Wenzel
    TI__Guru**** 183551 points

    Both TS3DV642 and TMDS351 will work without the level shifter. But beyond functional consideration in a design, in the examples I gave, one is taken the HDMI compliance into consideration and the other example is taken source/sink IO input voltage requirement into consideration.

    Thanks

    David